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A variety of lightoff and sweep tests were developed to characterize the performance of three-way catalysts using a computer-controlled laboratory reactor. Both fresh and thermally aged pelleted catalysts were characterized using these lightoff and sweep tests. For all of the lightoff and sweep tests, the aged catalyst showed a loss of performance when compared to the fresh catalyst. Although the tests which use a cycled environment show better agreement with engine dynamometer tests, the non-cycled tests were generally better able to distinguish between fresh and thermally aged catalysts. These results imply that while the laboratory reactor can perform tests which closely simulate the dynamic behavior of engine exhaust under closed-loop control, non-cycled tests may be more useful in ranking catalysts for durability.

A matrix of pelleted catalysts composed of Pt, Pd, Pt co-impregnated with Pd, and Pt physically mixed with Pd supported on A l2O3 were compared with the same noble metal formulations supported on CeO2/Al2O3 for lightoff and warmed-up performance in net lean exhaust. These catalysts were tested as prepared (fresh) and following a relatively severe thermal aging treatment (cycled between net lean and net rich environment at 1000°C for 4 h). Pd showed better lightoff performance than Pt for catalyzing the oxidation of propylene, while Pt showed better lightoff and warmed-up performance than Pd for catalyzing the oxidation of propane. Having both Pt and Pd present as a result of co-impregnation or physical mixture results in good lightoff and warmed-up performance for the conversion of both types of hydrocarbons. The presence of CeO2 generally decreases lightoff performance for most of these catalysts.

A Cu/ZSM-5 catalyst has been tested in both the laboratory and in a gasoline-fueled, lean-burn car. This catalyst is generally believed to be the current “state of the art” for removing NOx from lean engine exhaust. The laboratory tests showed that the HC species was the exhaust component which reduced the NOx. This catalyst actually produced CO, but the CO had no impact on the NOx reduction. The NOx conversion was inhibited by oxygen at oxygen levels below 4%, but was also modestly inhibited by oxygen levels above 4%. The NOx, conversion of these catalysts was less affected by SO2 than were the HC and CO conversions. These catalysts showed very poor thermal durability, losing much of their activity after aging under conditions milder than those typically used for three-way catalysts. The vehicle tests of the fresh Cu/ZSM-5 catalyst showed between 30 and 40% average NOx conversion.

Three vehicle and dynamometer-aged converters were evaluated for performance using the warmed-up portion (termed the “hot-18” cycles) of the Federal Test Procedure (FTP) and during a steady-state cruise using low and high sulfur content fuel. During the steady-state tests the catalyst performance was also monitored using two oxygen sensors designed to satisfy Phase II On-Board Diagnostics (OBD-II) requirements for vehicles sold in California in MY 1994 and thereafter. The performance of two of the converters decreased significantly upon switching to the high sulfur content fuel, and one of the converters which was diagnosed as passing with low sulfur fuel was diagnosed as failing with high sulfur fuel.

The following study was performed to investigate the in-use emissions performance of a California TLEV equipped with components aged in customer service on an enhanced I/M test. Fuels and ambient temperature conditions were chosen to compare I/M test conditions typical for California (moderate temperature on California Phase II gasoline) to those likely to be encountered in a Northeastern state (cold temperature on Winter grade fuel). To obtain repeatable results and simulate typical customer driving prior to the test, Bag II of the FTP schedule was used to simulate urban driving to an I/M lane, followed by a variable length idle to simulate waiting for the I/M test, followed by the IM240 test.

Catalysts taken from the lightoff and underfloor converters of two 1986 Corvette exhaust systems which had been vehicle-aged for 100,000+ miles were cut into 1″ thick sections along their axis and characterized for lean lightoff and warmed-up performance using a laboratory reactor. Sections were then treated to remove the poisons, and the characterization was repeated. An axial gradient in both lightoff and warmed-up conversion efficiency for HC and CO was detected within the first 2″ of both lightoff converters for both vehicles. This activity gradient is in agreement with the gradient in the phosphorus and zinc concentrations found in the front 2-3″ sections of the lightoff converters.

The performance of the OBD-II catalyst monitor of a 2.2 Corsica TLEV was investigated while operating on fuels with differing sulfur levels. Testing was performed using a driving schedule producing operating conditions which were acceptable to the production OBD-II system for active diagnosis of catalyst performance. During each test, catalyst diagnostic data and emissions performance data were collected simultaneously. Tests were performed at 22° C using California Phase II (35 ppm sulfur content) and Indolene clear (470 ppm sulfur content) fuels, and at 4°C using a commercial oxygenated Winter fuel (320 ppm sulfur content). Four dynamometer-aged converters were using in the testing. Converter performance in the form of HC conversion efficiency was found to generally decrease when the sulfur content in the fuel was increased.

This paper describes an investigation of the impact of various fuels, soak and test conditions on the emissions performance of a MY1996 Corsica TLEV on an IM240 test. The study also probes the impact of turning the engine off just prior to the IM240 test under these conditions. We found using a Wintertime federal fuel with a sulfur content of 485 ppm that the HC, CO and NOx emissions were increased when compared with similar tests at the same temperature of 16°C using the California Phase 2 fuel with a sulfur content of 32 ppm. When tests using the Wintertime fuel were performed at temperatures lower than 16°C, the emissions increased dramatically. In control tests, the engine ran at a constant idle for 15 min. prior to the IM240 with no engine turn-off. However, when the engine was turned-off just prior to the IM240, slight increases in tailpipe emissions resulted at 23°C and 16°C using California RFG.

Pelleted and monolith three-way catalysts were treated in a laboratory reactor under conditions closely simulating automobile exhaust and then characterized using x-ray photoemission and temperature programmed desorption techniques to determine relative amounts and oxidation states of sulfur stored by the catalyst. Sulfur originating as SO2 in the feed was stored on the support component of both catalysts in the form of adsorbed sulfates and sulfites and on the noble metals in the form of elemental sulfur. The monolith catalyst stored a greater amount of sulfur and equilibrated more rapidly with the sulfur content in the feed than did the pelleted catalyst. Operation in a rich environment removes sulfur from the support components, while operation in a lean environment removes sulfur from the noble metal surfaces. This behavior is consistent with the observation that sulfur inhibits three-way activity in a rich environment.